Coin acceptor/rejector

ABSTRACT

Coins are tested by inserting them into an oscillator driven tank circuit resonating at near or equal frequency when the proper coin influences particularly the tank circuit. A narrow amplitude detection band and flat spiral tank circuit coils of coin-like diameter limit the response to particular coins. The oscillator includes a similar tank circuit and both tank circuits are subjected to the same environment.

United States Patent [1 1 Klinger Aug. 26, 1975 [54] COINACCEPTOR/REJECTOR 3,796,295 3/1974 Montolivo et a1. 194/100 A [76]Inventor: Lance T. Klinger, 81 1O Redlands,

APL 307 playa Del Rey, C ]if Primary Examiner-Allen N. Knowles 2Attorney, Agent, or Firm-Ralf H. Siegemund 9 91 I [22] Filed: Mar. 11,1974 57 B A [21] Appl. No.: 450,088 1 A STR CT Coins are tested byinserting them into an oscillator driven tank circuit resonating at nearor equal fre- [52] Cl 194/100 A; 324/34 gags 1 quency when the propercoin influences particularly [51] Int. Cl. R /9 i the tank circuit Anarrow amplitude detection band [58] held of Search 194/100 and flatspiral tank circuit coils of coin-like diameter 324/34 73/163 209/81 Alimit the response to particular coins. The oscillator includes asimilar tank circuit and both tank circuits [56] g NT are subjected tothe same environment.

UNITED TA S ATE S 3 599 771 28 Claims, 6 Drawing Figures 8/1971Hinterstocker 194/100 A Mill/V7700; new! rue (wax/r rmv/m z-wr;

PATENTED MJEZSIQIS 3, 9 O1 ,3 6 8 sum 2 UF 2 1 COIN ACCEPTOR/REJECTORBACKGROUND OF THE INVENTION The present invention relates to a coindetecting, discriminating and testing apparatus or device and moreparticularly to apparatus for testing a coin and accepting or rejectingit. Such an apparatus is to be used in coin operated vending machines orother equipment or mcahines, which are coin operated.

A coin operated machine is usually equipped with a device that tests anycoin which is being entered. The slot in the machine, through which acoin in inserted, has usually particular dimensions preventing at leastlarger coins for being inserted. Beyond the slot equipment of one kindor another is provided to test the coin so as to prevent coins of wrongdenomination, foreign coins or slugs, from operating the machine.

Many types of testing equipment are known here, trying to discriminatethe proper coin from others or slugs on the basis of electrical and/ormagnetic properties, and/or weight and/or size. Unfortunately, closesimilarities between a proper coin and many improper ones require ratherdelicate testing; the range of test values of whatever characteristicsis being used and defining or establishing the criterium for acceptanceor rejection is extremely narrow. Slugs, of course, are the greatestproblem, as they can be made at will to resemble a proper coin as muchas the forger wants it to. But also foreign coins often resemble closelydomestic ones. The quarter, for example, seems to have a size thatamounts almost to a kind of world-wide standard size for coins. Coindiscrimination is, therefore, a difficult problem, indeed. Needless tosay that methods can be devised and equipment can be designed testingall conceivable properties of a coin to sort the proper ones from therest. However, little is gained in practice, if the input structure of acoin-operated machine is converted into a miniature laboratory.

Among the various methods tried, many are based on the principle ofelectromagnetic interaction between the coin and an inductance, in thatthe coin modifies the inductiv-ity of a sensor coil. Reference is madehere to the US. Pat. Nos. 3,152,677; 3,373,856; 3,401,780; 3,481,443;3,561,580; 3,506,103; 3,576,244; 3,741,363 and 3,749,220.

It was found, however, that little attention has been given in the pastto changes in the environment in which the apparatus is operated.Changes in tempera ture and humidity coupled with abuse (changing forexample positional adjustments), may result in significant Changes inthe operating parameters of the testing equipment. Hence, itssensitivity must be reduced to permit compensation, but that in turnmakes inevitable that some false coins are accepted; the equipment hasto be de-sensitized to such an extent that a change in ambientconditions will not produce equipment changes which would place a goodcoin outside of the accept range.

SUMMARY OF THE INVENTION It is an object of the present invention toprovide a coin accept reject apparatus, which is very sensitive butwhose sensitivity range adjusts with changes in am-' tion between a coinand an inductance, but that interaction is processed in a mannerdifferent from approaches taken in the past.

It is a further object of the present invention to provide a new andimproved coin discriminating circuit, which can be used upon appropriateselection of parameters to discriminate different kinds of coins onbasis of the same principle.

In accordance with the preferred embodiment of the present invention, itis suggested to use an oscillator with a first tuned circuit, such as atank circuit providing an electrical signal of a particular frequencyand at a Q as high as possible. A second tuned circuit is connected tothe oscillator for being energized therefrom to develop a particularamplitude signal when a proper coin has (temporily) particulardisposition to the coil (or coils) of the first or second tank circuit.

In the preferred form the second tuned circuit with adjacent proper coinresonates at or near the frequency of the oscillator (and of the firsttuned circuit). The sensor coils as well as the oscillator coils areplaced alongside a chute or the like, through which coins will drop, butthe coils of the different, tuned circuits are decoupled as much aspossible and the first tuned circuit does not sense the coin when sensedby the second tuned circuit. The two tuned circuits are, therefore,placed into similar environmental conditions as much as possible withoutproducing mutual coupling. Therefore, the two tank circuits will trackeach other.

The discriminating circuit includes additional circuitry forestablishing a rather narrow detection band of signal amplitudes, andthe voltage across the second tuned circuit when constructed as tankcircuit must fall in that band for a coin to be recognized asacceptable. A high Q of the sensor circuit results in large changes inthe amplitude of the voltage across the second tuned circuit, if a tankcircuit, even for small changes in the inductance of the sensor coil,provided the oscillator frequency is rather close to the resonance peakof the tuned sensor circuit. As a consequence, the detection of whetheror not the amplitude falls within the narrow detection band, is verysensitive while, on the other hand, the detected signals and the bandtrack each other. Specifically, the circuitry is designed so that theband tracks the environment and/or any changes in supply voltage.

It is another feature of the invention that the coil or coils, at leastof the second tuned circuit, are constructed as a flat spiral, printedcircuit coil or coils having an outer diameter about equal to thediameter of a coin to be accepted and having coaxial disposition to thecoin when in sensing position. Such an arrangement provides maximumsensitivity, as eddy currents flow in a circumferential path in thecoin. The dimension of a coin passing the sensing coil or coils will,therefore, materially influence the effective inductance at the instantof passage through a coaxial position with respect to such coil orcoils.

The preferred form of practicing the invention provides for particularresponse of the sensing tank circuit with juxtaposed coin to aparticular frequency as determined by the oscillator, and hereparticularly by the tank circuit thereof. It is, however, possibie tooperate with a fixed response of the sensing circuit in all cases, withno coin in its tank circuit, while the coin influences the oscillatortank circuit and causes a particular frequency to be generated; theresponse of the sensing circuit to that frequency is then used asindicator.

It was found that a coin discrimination circuit constructed inaccordance with the present invention is very selective and retains thatselectivity under a width range of ambient conditions.

DESCRIPTION OF THE DRAWINGS While the specification concludes withclaims particularly pointing out and distinctly claiming the subjectmatter which is regarded as the invention, it is believed that theinvention, the objects and features of the invention and furtherobjects, features and advantages thereof will be better understood fromthe following description taken in connection with the accompanyingdrawings in which:

FIG. 1 is a schematic elevation of a coin accept/reject device, whereinthe coin must pass through a particular path to be accepted;

FIG. lb is a section along 1b 1b in FIG. 1;

FIG. 2 is a circuit diagram of an example of the preferred embodiment ofthe present invention;

FIG. 3 is a voltage vs. frequency characteristics of a tank circuitincluded in the circuit of FIG. 2;

FIG. 4 is a voltage vs. time diagram showing in different sectionsdifferent cases and examples of tank circuit voltage of coin sensing ascarried out by the circuit of FIG. 2; and

FIG. 5 shows a characteristic, similar to FIG. 3 but with a slightmodification.

Proceeding now to the detailed description of the drawings, FIG. 1 showsa rather flat casing 10, which includes internal dividers to define apathway 11 for a coin, with two exit branches 11a and 1112. A mechanicalswitch or gate 12 determines whether a coin is permitted to pass throughthe accepted branch 11a or must exit through the rejected branch 11b.The switch 12 is solenoid operated, and the solenoid is operated by thecoin test circuit depicted as circuit diagram in FIG. 2.

The circuit is packaged to a large extent and contain miniaturizedcircuit elements to be described in detail below. The mechanical aspectof coin acceptance and rejection is not part of the present invention;the patents mentioned above show various kinds of mechanisms, which canbe used. Many others are well-known.

As will become apparent shortly, the coin test circuit includes twogroups of coils l4 and disposed in close proximity to each other. Thefact that coils 14 are also placed along the entrance sections of chuteor duct 11 is incidental, but the placement of coils 15 is critical. Thegroup of coils 15 includes four coils each constructed as a printedcircuit spiral and mounted in pairs on both sides of two thin pc boards16. The two boards are placed alongside chute 11, on the outside and insuch disposition that the center axes of all four coils l5 coincide. TheThe coils 15 have a common axis transverse to chute 11. The same is truefor the group of coils 14 but the groups of coils 14 and 15 aredecoupled.

The spiral coils 15 each have a diameter quite accurately similar to thediameter of a coin of the type to be accepted when placed into thechute. Since the four coils 15 are coaxial and concentrically mountedadjacent to and alongside of chute 11, a coin of the proper diameterwill pass the coils 15, so that the center of the coin will,approximately at least, run through the common axis of the coils, whilethe periphery of the coin is aligned with the periphery of the coils inthe same instant.

While the relation as described is basically arbitrary, it can readilybe seen that in the instant of coaxial passage of a coin of the propertype, a very unique inductivity is established. That inductivity dependson the size, the resistivity and permeability of the coin material, theamount of the material and, possibly, the distribution of the materialwithin the coil. The spiral sensing coils 15 when positioned parallel tothe coin, cause maximum sensitivity to those properties of a coin, whichare effective in the electromagnetic interaction. The eddy currents flowin a circumferential path in the coin.

The particular disposition of coils 14 in relation to the disposition ofcoils 15 is relevant in the following respect. First, in the negativesense, the coin as such will not in the least influence the inductanceof coils 14 at the instant of passing through the coaxial dispositionwith regard to coils l5. Otherwise, it is important that coils 14 and 15are subjected to the same ambient con ditions such as temperature andhumidity. Therefore, changes in inductance on account of such ambientchanges are similar as to both coils; they both track each other. Ofadditional significance is here the shunt capacitance of the coils asdetermined by the dielectric constant of the material of casing 10. Bothcoil groups are affected similarly here due to the disposition on theoutside surface of casing 10 adjacent chute 11. Also, capacitors 26 and27 may have the same dielectric type with similar temperaturecharacteristics.

The two groups of coils l4 and 15 pertain to the coin test circuitdepicted in FIG. 2. The circuit includes, basically, an oscillator 20, asensing circuit 25, a threshold detector and a timer for controlling asolenoid, which in turn controls the lever, gate or switch 12 (FIG. 1).Elements 40 and 45 together constitute an amplitudedetector/discriminator to determine whether or not a particular signalas derived from tuned circuit 25 has amplitude within a narrow range(amplitude detection band).

The oscillator includes two transistors 21 and 22 with interconnectedemitters, which in turn connect to ground potential via a current source23, which in this I case is a simple resistor. The collector circuits ofthe two transistors are established by two tank circuits 24 and 25whereby tank circuit 24 is comprised of the coils l4 and of a capacitor26, while tank circuit 25 is comprised of the coils l5 and of acapacitor 27. Tank circuit 25 is the tuned sensing circuit of thesystem. The coils 14 are connected in series to each other, so are coils15. Tank circuit 24 is an example of the first tuned circuit, and 25 isan example of the second tuned circuit as referred to in theintroduction.

Thus far, the transistor circuits are symmetrical, however, a feedbacknetwork 30 comprised of a capacitor 31, and of two resistors 32, 33,together with a bias as applied to the base circuit of transistor 21,provides for oscillator operation at a frequency determined by tankcircuit 24. A resistor-diode resistor circuit 34, 35, 36 defines a biasvoltage for transistor 21 and that bias, together with the resistor 23,establishes the emitter current for both transistors.

The L-C values of tank circuit 24 define a particular frequency, andpositive feedback of 31-32 produces oscillations at that frequency WPursuant to these oscillations the flow of current 1 alternates betweentransistors 21 and 22. It should be noted, that the tank circuits areout of phase accordingly. and their phase difference could be used as anindication whether or not a proper coin is used inbetween coils 15.However in the present case, the amplitude of the signal across tankcircuit 25 is monitored.

As a consequence of the fluctuation of current flow through transistor22, an oscillating current of welldefined magnitude is driven through(load) tank circuit 25. This tank circuit contains the sensor coils 15.The voltage across the tank circuit 25 (from constant current I) dependsonly on the frequency of the oscillator in relation to the resonancefrequency and the Q of the tank circuit. Additionally, (and mostimportantly), the voltage across 25 depends on absence or presence of aproper coin in the coaxial sensing position relative to coils 15.

It should be noted that the two tank circuits are not components of abridge circuit, nor is tank circuit 25 included in a feedback loop ofthe oscillator. Rather, the transistor with common emitter currentsource can be deemed an amplifier, whose input is provided by feedback(plus bias) and which has a double ended output (collectors of thetransistors), to which are connected the two different tank circuits 24,25.

FIG. 3 depicts the voltage (V across the tank cir cuit 25 in response tofrequency. The fully drawn characteristic is plotted under theassumption of a variation of the oscillation frequency in accordancewith the values plotted on the abscissa, whereby it is assumed fur therthat a proper coin, i.e. a coin of the type to be accepted, is in thecoil in axial alignment therewith. The dotted curve represents the casewhen the true coin is absent, and no coin or other magnetizable metal(slug) is in the slot 11 between the portions of the coils 15 on eitherside of the slot. The resonance peak in the latter case is considerablydisplaced from the resonance peak of the proper coin case".

It shall now be assumed that the oscillation frequency W is adjusted tocoincide with the resonance peak frequency W., of tank circuit 25.Therefore, the peak voltage across the tank in accordance with thecharacteristics can and will develop when, but only when, a proper coinis in the slot (or passes through). A coin of a different metal alloy ordifferent dimensions will result in a higher or lower voltage acrosstank circuit 25)- One can see from HO. 3 that the tuned tank circuit 25with proper coin has a particular sensitivity frequency band about thepeak frequency W, and the oscillator frequency W,,,,,. is not onlyin-that band, but in the center thereof. A high Q of circuit 25 resultsin a narrow band width. With no coin inbetwcen coils 15, the band isshifted to a frequency range quite remote from the oscillator frequency.W represents the resonance frequency of circuit 25 with no coin or slugin coils 15.

The voltage across tank circuit 25, (but taken relative to ground) ismonitored by a circuit which includes a diode 37 and a pair of seriallyconnected resistors 38, 39. This circuit cooperates with thresholddetector 40,

which includes two differential amplifiers or comparators, 41 and 42.

Each comparator receives the same bias voltage V derived from thevoltage source V by a voltage divider network 43/44, but the signalinput of each comparator is not the same, the resistor 38 represents thedifference of response. Together with comparators 41, 42, resistor 38establishes a particular response band.

By virtue of the common bias V of the comparators, the two comparatorswill change state for the same voltage when applied to the respectivesignal input terminal, but due to the voltage drop across resistor 38comparator 42 will not change state at the same voltage across tankcircuit 25 which causes comparator 41 to change state and vice versa.This difference in response to tank circuit voltage V is the amplitudedetection band of the system. Hence a voltage peak which reaches thatband will trigger one of the comparators but not the other one, voltagesoutside of that band will trigger both or neither.

The timer 45 provides an output pulse of sufficient width to drive thesolenoid given an input from comparator 42. One or more output pulses ofcomparator 42, defining an unequal state, as compared with the otherwill trigger timer 45 to drive the solenoid that controls the coin gate12 (FIG. 1).

Thus, FIG. 4 shows the voltage band AV generally described above andhaving the following specific significance. The upper boundary of theband AV is given by V For V,,- V comparator 41 is in one state, for V Vcomparator 41 is in the other state. The band width voltage AVrepresents the voltage drop across resistor 38, and the signal voltageeffective at comparator 42 is V A while the reference, of course, is thesame, namely V Hence for V V +AV comparator 42 is in one state, for VVR+AV comparator 42 is in the opposite state.

Case (a) in FIG. 4 represents the fluctuating voltage V,,- when there isno coin in or passes through the tank circuit. The small amplitude ofthe fluctuation corresponds to the dotted characteristics in FIG. 3.Case (b) represents the fluctuations occurring, for example, when thecoin does not decrease inductance l5 enough. In both cases. (a) and (b),neither of the comparators 41, 42 change state, i.e. they are in thenormal state. I

Case (c) in FIG. 4 represents the situation where a coin reducesinductance 15 more than the material for a desired coin. The voltagefluctuations are larger, so that both comparators change state. They donot change state simultaneously, but one shortly after the other, 42before 41, but 41 causes the timer to be reset before the solenoid canrespond to the output initiated by comparator 42.

The circuit is now adjusted that only a proper coin will produce case((1). In this case, the voltage excursion minima terminate in the bandAV. In other words, comparator 42 changes state, but not comparator 41.A desired coin, i.e. one that is to be accepted, will, therefore,produce a situation, in which temporarily comparator 42 changes stateand 41 does not change state.

Circuit 45 responds to the unequal state of comparators 41/42 andproduces a control signal of sufficient duration for actuating thesolenoid, which in turn triggers the switch 12. In FIG. 4 case (d),comparator 42 changes state and triggers the timing circuit 45 whichdrives the solenoid for a defined duration. In FIG. 4 case comparator 42changes state first and triggers the timing circuit 45. In case (c),comparator 41 changes state soon after comparator 42, and thereby resetsthe timing circuit 45 long before the solenoid has received sufiicientenergy to actuate the coin switch.

The operating conditions as described thus far use exact equality ofoscillation frequency and of sensor tank resonance frequency for aninserted proper coin. Hence, the tank circuit 25 is operated on theresonance peak of FIG. 3; the bias and detection band (FIG. 3) areattuned accordingly. One can, however, use a slightly larger oscillationfrequency, so that the detection band is located on the higher frequencyflank of the characteristics as plotted in FIG. 5. This mode ofoperation allows capacitor trimming for circuit irregularities, as thefinal adjustment is the appropriate placement of the detection band,which amounts merely to fine trimming of the resistor 23 or capacitor26. The dotted curve represents again the characteristics of the tankcircuit with no coin between coils 15.

Another embodiment of this invention would have the oscillatorinductance 14 greater than inductance 15. In this case, detection wouldoccur at coil 15 when the coin passed through coil 14. In this case onlya proper coin will produce an oscillator frequency so that the resultingresponse in sensing coil 15, but with no coin in its proximity, willproduce an amplitude V which is right in the detection band. Thisembodiment also rejects voltage and environment changes, but is lesspreferred, because the Q of the oscillator tank circuit is slightlydegraded in that mode of operation.

The placement of the coils 14 and 15 in close proximity causes them totrack each other, i.e. the oscillation frequency and the sensor tankvary similarly under changes in temperature and/or humidity. The diodeshould match transistors 21, 22, which presents no problem in an ICimplementation, so that the temperature dependancy of the oscillationtransistors is ofiset by a corresponding temperature dependancy of thebias. Diode 37 in turn tracks diode 35 to render the amplitude detectionindependent from temperature variations in the circuit. The voltagethreshold, i.e. the effective response level and placement of thedetection band V is independent from the voltage supply +V, at least tothe first order. The amplifier current I as derived from the currentsource is dependent upon the value of voltage V and varies therewith tothe same extent. This increases the ac. component of V; in an amount andby a direction (sign) equal to the change in threshold as defined by thebias circuit 43/44. Hence, the means establishing the band track andchanges in voltage and in sensing signal as derived from tank circuit25.

Returning briefly to FIG. 1 in conjunction with FIG. 2, one can see thatthe distinction between coin accept- /reject situations has differentconsequences for coin guidance by operation of switch 12. In addition,thereto, or in lieu thereof, one can provide an indication, visual orotherwise, for example, in form of lamps identifying whether or not agood coin has been presented for testing.

The invention is not limited to the embodiments described above but allchanges and modifications thereof not constituting departures from thespirit and scope of the invention are intended to be included.

I claim:

1.'A coin testing device comprising:

an oscillator producing a signal of a particular frequency at arelatively high Q and of a narrow band;

a resonating sensing circuit including at least one coil disposed, sothat a coin to be tested will particularly change and determine theresonance frequency of the sensing circuit, when having a particulardisposition with respect to the coil;

the sensing circuit being connected electrically to be energized by theoscillator without inductive coupling through said coil;

the sensing circuit having a narrow response characteristic band aboutsaid resonance frequency, when sensing a coin, the oscillation frequencybeing in said band;

the sensing circuit having a frequency response band remote from saidoscillation frequency band when no coin is in its sensing range; and

circuit means connected to said sensing circuit for detecting theresponse of the circuit to the oscillations in the presence or absenceof a coin.

2. A coin testing device as in claim 1, wherein the circuit meansincludes an amplitude detector/discriminator for detecting whether thevoltage of the sensing circuit has a particular amplitude within anarrow range in representation of a particular type of coin to bedetected.

3. A coin testing device as in claim 1, wherein the sensing circuit is atank circuit, the circuit means connected to be responsive to theamplitude of the voltage across the tank circuit.

4. A coin testing device as in claim 2, the circuit means includingcomparator means defining a detection band for response to saidamplitude.

5. A coin testing device as in claim 1, wherein the oscillationfrequency equals the resonance frequency of the sensing circuit when acoin is adjacent thereto.

6. A coin testing device as in claim 1, wherein the oscillationfrequency is slightly higher than the peak frequency of the resonanceband of the sensing circuit when a coin is adjacent thereto.

7. A coin testing device as in claim 1, the sensing means including atleast one flat spiral coil having outer diameter about equal to thediameter of a coin to be detected, the particular disposition being aconcentric one as between the coin and the coil.

8. A coin testing device comprising:

an oscillator including a first tuned circuit with at least one coil forproducing an oscillator signal at a relatively high Q and having thefrequency of the resonance frequency of the tuned circuit;

a second tuned circuit including at least one coil and connected to beenergized by the oscillator so that a sensing voltage is derivable fromthe second 9 tuned circuit whose amplitude depends 6d the frequency ofthe oscillator;

the respective resonance frequences of said first and second tunedcircuit having a particular difference when no coin is in thevicinityof. the coil of either of the tuned circuits; 7

a particular type of coin when in particular juxtaposed disposition toone of the coils causing a change in the resonance frequency of thetuned circuit to which the coil pertains, the change being operative todiminish said difference so that said amplitude assumes increased value;and

circuit means providing for a particular amplitude detection band andconnected to the second tuned circuit to determine whether or not saidincreased amplitude falls into said detection band.

9. A coin testing device as in claim 8 wherein the other one of saidcoils has disposition so that the coin may pass in its vicinity whereupon said difference is increased.

10. A coin testing device as in claim 9, wherein the coils of the firstand second circuits are located along a path for a coin, in closeproximity to each other but in magnetically decoupled relationship.

11. A coin testing device as in claim 8, wherein the oscillator includestwo emitter coupled transistors with a common current source, and afeedback circuit from the collector of one of the transistors to thebase of the other one of the transistors, the oscillator furtherincluding a first tank circuit in the collector circuit of one of thetransistors as the first tuned circuit second tuned, while the circuitis a second tank circuit connected to the collector of the respectiveother one of the transistors.

12. A coin testing device as in claim 10, including atemperature-dependent bias for the transistors, the circuit meansincluding means for tracking the temperature dependency of theoscillator and of the bias.

13. A coin detector as in claim 11, wherein the circuit means includesmeans for amplitude tracking of the detection band.

14. A coin detector, comprising:

an oscillator producing a signal of a particular frequency;

sensing means connected to the oscillator including at least onecircular flat spiral coil having at least approximately the samediameter as the coin to be detected, and being disposed so that the coinwill pass the coil coaxially, whereupon the coil as coupled to the coinassumes a particular inductivity; and

circuit means connected to be responsive to the voltage across the coilfor detecting the coin.

15. A coin detector as in claim 14, wherein the oscillator includes alsoat least one spiral coil, the spiral coils being mounted along a travelpath for the coin to be subjected to similar environmental conditions,the coil of the sensing means and the coil of the oscillator beingdecoupled electromagnetically.

16. A coin detector as in claim 14, wherein the sensing means includesat least two coils, each being of'spiral configuration and of similardiameter and coaxially disposed to each other, so that the coin passesbetween them.

17. A coin detector as in claim 14, wherein the circuit means includes acapacitor connected to the coil and completely therewith a resonancecircuit, whose resonance band includes the oscillation frequency.

18. A coin detecting device comprising:

an amplifier with double-ended output, and an input;

a first tuned circuit connected to one of said outputs, a feedbackcircuit between said one output and said input for establishing anoscillator, whose frequency is determined by the first tuned circuit;

a second tuned circuit connected to the other one of said outputs, oneof said first and second tuned circuits located so that a coin to bedetected and when in particular disposition to the one tuned circuitmaterially determines its tuned frequency, being the same orapproximately the same frequency as the frequency of the other one ofthe tuned circuits; and

circuit means connected to the second tuned circuit for detecting theamplitude of a signal developed by the second tuned circuit uponoscillation of the oscillator.

19. A coin detector as in claim 18, wherein the circuit means includesan amplitude band detector means, the amplitude of the signal developedby the second tuned circuit, when sensing a proper coin falling intothat band.

20. A coin detector as in claim 18, wherein the sec ond tuned circuit istuned to a frequency relative to the oscillation frequency, so that theamplitude of the signal varies significantly forsmall differences in oneof the parameters of the second tuned circuits.

21. A coin detector as in claim 18, the circuit means including a pairof comparators biased for slightly different changes of state toestablish an amplitude detection band, the bias being provided throughcircuitry from a voltage source, being the same source operating saidamplifier to obtain mutual tracking of the band and of the signal.

22. A coin detector as in claim 18, wherein the resonance frequency ofthe first tuned circuit is higher than the resonance frequency of thesecond tuned circuit with no coin influencing either tuned circuit, theparticular disposition of a proper coin being in the vicinity of thesecond tuned circuit chaning the resonance frequency of the second:tuned circuit to a value close to the resonance of the first tunedcircuit.

23. A coin detector as in claim 18, wherein the resonance frequency ofthe second tuned circuit is higher than the resonance frequency of thefirst tuned circuit with no coin influencing either tuned circuit, theparticular disposition of a proper coin being in the vicinity of thefirst tuned circuit changing the resonance frequency of the first tunedcircuit to a value close to the resonance of the second tuned circuit,so that the oscillator frequency is altered accordingly.

24. A coin testing device comprising:

an oscillator including'a first tuned circuit with at least one coil forproducing an oscillator signal at a relatively high Q and having thefrequency of the resonance frequency of the tuned circuit;

a second tuned circuit including at least one coil and connectedgalvanically to the oscillator to be energized therefrom, while thecoils of the two tuned circuits are spaced apart to be magneticallydecoupled;

each of said two circuits having a particular resonance frequency band,said bands being spaced apart when no coin is in the vicinity of eithercoil of the tuned circuits;

a particular type of coin when in particular juxtaposed disposition toone of the coils causing the frequency bands to be shifted into at leastpartially overlapping disposition;

first circuit means connected to said second tuned circuit to derivetherefrom a sensing voltage whose amplitude depends on the relativedisposition of said bands, increasing with increasing overlap; and

second circuit means connected to the first circuit means and providingfor a particular amplitude de tection band to determine whether or notsaid amplitude as derived falls into said detection band.

25. A testing device as in claim 24, wherein the bands overlap withcoinciding centers when a particular type of coin is adjacent to the onecoil.

26. A testing device as in claim 24, wherein the peak frequency of theoscillation band is slightly higher than the peak frequency of the bandof the second tuned circuit when a particular type of coin is adjacentto the one coil.

27. A testing device as in claim 24, the coils including at least oneflat spiral coil having outer diameter about equal to the diameter of acoin to be detected, the particular disposition being a concentric oneas between the coin and the coil.

28. A testing device as in claim 24, wherein the oscillator includes twoemitter coupled transistors with a common current source, and a feedbackcircuit from the collector of one of the transistors to the base of theother one of the transistors, the oscillator further including a tankcircuit as the first tuned circuit and connected in the collectorcircuit of one of the transistors, while the second tuned circuit is asecond tank circuit connected to the collector of the respective otherone of the transistors.

1. A coin testing device comprising: an oscillator producing a signal ofa particular frequency at a relatively high Q and of a narrow band; aresonating sensing circuit including at least one coil disposed, so thata coin to be tested will particularly change and determine the resonancefrequency of the sensing circuit, when having a particular dispositionwith respect to the coil; the sensing circuit being connectedelectrically to be energized by the oscillator without inductivecoupling through said coil; the sensing circuit having a narrow responsecharacteristic band about said resonance frequency, when sensing a coin,the oscillation frequency being in said band; the sensing circuit havinga frequency response band remote from said oscillation frequency bandwhen no coin is in its sensing range; and circuit means connected tosaid sensing circuit for detecting the response of the circuit to theoscillations in the presence or absence of a coin.
 2. A coin testingdevice as in claim 1, wherein the circuit means includes an amplitudedetector/discriminator for detecting whether the voltage of the sensingcircuit has a particular amplitude within a narrow range inrepresentation of a particular type of coin to be detected.
 3. A cointesting device as in claim 1, wherein the sensing circuit is a tankcircuit, the circuit means connected to be responsive to the amplitudeof the voltage across the tank circuit.
 4. A coin testing device as inclaim 2, the circuit means including comparator means defining adetection band for response to said amplitude.
 5. A coin testing deviceas in claim 1, wherein the oscillation frequency equals the resonancefrequency of the sensing circuit when a coin is adjacent thereto.
 6. Acoin testing device as in claim 1, wherein the oscillation frequency isslightly higher than the peak frequency of the resonance band of thesensing circuit when a coin is adjacent thereto.
 7. A coin testingdevice as in claim 1, the sensing means including at least one flatspiral coil having outer diameter about equal to the diameter of a cointo be detected, the particular disposition being a concentric one asbetween the coin and the coil.
 8. A coin testing device comprising: anoscillator including a first tuned circuit with at least one coil forproducing an oscillator signal at a relatively high Q and having thefrequency of the resonance frequency of the tuNed circuit; a secondtuned circuit including at least one coil and connected to be energizedby the oscillator so that a sensing voltage is derivable from the secondtuned circuit whose amplitude depends on the frequency of theoscillator; the respective resonance frequences of said first and secondtuned circuit having a particular difference when no coin is in thevicinity of the coil of either of the tuned circuits; a particular typeof coin when in particular juxtaposed disposition to one of the coilscausing a change in the resonance frequency of the tuned circuit towhich the coil pertains, the change being operative to diminish saiddifference so that said amplitude assumes increased value; and circuitmeans providing for a particular amplitude detection band and connectedto the second tuned circuit to determine whether or not said increasedamplitude falls into said detection band.
 9. A coin testing device as inclaim 8 wherein the other one of said coils has disposition so that thecoin may pass in its vicinity where upon said difference is increased.10. A coin testing device as in claim 9, wherein the coils of the firstand second circuits are located along a path for a coin, in closeproximity to each other but in magnetically decoupled relationship. 11.A coin testing device as in claim 8, wherein the oscillator includes twoemitter - coupled transistors with a common current source, and afeedback circuit from the collector of one of the transistors to thebase of the other one of the transistors, the oscillator furtherincluding a first tank circuit in the collector circuit of one of thetransistors as the first tuned circuit second tuned, while the circuitis a second tank circuit connected to the collector of the respectiveother one of the transistors.
 12. A coin testing device as in claim 10,including a temperature-dependent bias for the transistors, the circuitmeans including means for tracking the temperature dependency of theoscillator and of the bias.
 13. A coin detector as in claim 11, whereinthe circuit means includes means for amplitude tracking of the detectionband.
 14. A coin detector, comprising: an oscillator producing a signalof a particular frequency; sensing means connected to the oscillatorincluding at least one circular flat spiral coil having at leastapproximately the same diameter as the coin to be detected, and beingdisposed so that the coin will pass the coil coaxially, whereupon thecoil as coupled to the coin assumes a particular inductivity; andcircuit means connected to be responsive to the voltage across the coilfor detecting the coin.
 15. A coin detector as in claim 14, wherein theoscillator includes also at least one spiral coil, the spiral coilsbeing mounted along a travel path for the coin to be subjected tosimilar environmental conditions, the coil of the sensing means and thecoil of the oscillator being decoupled electromagnetically.
 16. A coindetector as in claim 14, wherein the sensing means includes at least twocoils, each being of spiral configuration and of similar diameter andcoaxially disposed to each other, so that the coin passes between them.17. A coin detector as in claim 14, wherein the circuit means includes acapacitor connected to the coil and completely therewith a resonancecircuit, whose resonance band includes the oscillation frequency.
 18. Acoin detecting device comprising: an amplifier with double-ended output,and an input; a first tuned circuit connected to one of said outputs, afeedback circuit between said one output and said input for establishingan oscillator, whose frequency is determined by the first tuned circuit;a second tuned circuit connected to the other one of said outputs, oneof said first and second tuned circuits located so that a coin to bedetected and when in particular disposition to the one tuned circuitmaterially determines its tuned frequency, being the same orapproximately tHe same frequency as the frequency of the other one ofthe tuned circuits; and circuit means connected to the second tunedcircuit for detecting the amplitude of a signal developed by the secondtuned circuit upon oscillation of the oscillator.
 19. A coin detector asin claim 18, wherein the circuit means includes an amplitude banddetector means, the amplitude of the signal developed by the secondtuned circuit, when sensing a proper coin falling into that band.
 20. Acoin detector as in claim 18, wherein the second tuned circuit is tunedto a frequency relative to the oscillation frequency, so that theamplitude of the signal varies significantly for small differences inone of the parameters of the second tuned circuits.
 21. A coin detectoras in claim 18, the circuit means including a pair of comparators biasedfor slightly different changes of state to establish an amplitudedetection band, the bias being provided through circuitry from a voltagesource, being the same source operating said amplifier to obtain mutualtracking of the band and of the signal.
 22. A coin detector as in claim18, wherein the resonance frequency of the first tuned circuit is higherthan the resonance frequency of the second tuned circuit with no coininfluencing either tuned circuit, the particular disposition of a propercoin being in the vicinity of the second tuned circuit chaning theresonance frequency of the second tuned circuit to a value close to theresonance of the first tuned circuit.
 23. A coin detector as in claim18, wherein the resonance frequency of the second tuned circuit ishigher than the resonance frequency of the first tuned circuit with nocoin influencing either tuned circuit, the particular disposition of aproper coin being in the vicinity of the first tuned circuit changingthe resonance frequency of the first tuned circuit to a value close tothe resonance of the second tuned circuit, so that the oscillatorfrequency is altered accordingly.
 24. A coin testing device comprising:an oscillator including a first tuned circuit with at least one coil forproducing an oscillator signal at a relatively high Q and having thefrequency of the resonance frequency of the tuned circuit; a secondtuned circuit including at least one coil and connected galvanically tothe oscillator to be energized therefrom, while the coils of the twotuned circuits are spaced apart to be magnetically decoupled; each ofsaid two circuits having a particular resonance frequency band, saidbands being spaced apart when no coin is in the vicinity of either coilof the tuned circuits; a particular type of coin when in particularjuxtaposed disposition to one of the coils causing the frequency bandsto be shifted into at least partially overlapping disposition; firstcircuit means connected to said second tuned circuit to derive therefroma sensing voltage whose amplitude depends on the relative disposition ofsaid bands, increasing with increasing overlap; and second circuit meansconnected to the first circuit means and providing for a particularamplitude detection band to determine whether or not said amplitude asderived falls into said detection band.
 25. A testing device as in claim24, wherein the bands overlap with coinciding centers when a particulartype of coin is adjacent to the one coil.
 26. A testing device as inclaim 24, wherein the peak frequency of the oscillation band is slightlyhigher than the peak frequency of the band of the second tuned circuitwhen a particular type of coin is adjacent to the one coil.
 27. Atesting device as in claim 24, the coils including at least one flatspiral coil having outer diameter about equal to the diameter of a cointo be detected, the particular disposition being a concentric one asbetween the coin and the coil.
 28. A testing device as in claim 24,wherein the oscillator includes two emitter - coupled transistors with acommon current source, and a feedback circUit from the collector of oneof the transistors to the base of the other one of the transistors, theoscillator further including a tank circuit as the first tuned circuitand connected in the collector circuit of one of the transistors, whilethe second tuned circuit is a second tank circuit connected to thecollector of the respective other one of the transistors.